The present invention relates to a one-way valve. More particularly the invention relates to a one-way valve which is characterized by novel features of construction and arrangement so that it is very sensitive to pressure differentials and which is extremely reliable in operation. For these reasons it is particularly useful in certain types of surgical and laboratory systems, such as blood collecting systems.
In accordance with some typical prior art techniques for drawing blood samples, a syringe consisting essentially of a barrel with a plunger and a needle at one end is used. The nurse or technician prepares the patient in the conventional fashion by applying a tourniquet and when the vein is raised simply inserts the needle into the vein and draws the plunger rearwardly to create a vacuum which then draws blood into the syringe. The nurse then expels the contents of the syringe into a tube which is sealed and then is ready for further processing. This system has certain disadvantages and drawbacks. For example, if the syringe plunger is pulled back roughly or with too much pressure, currents are created in the blood which break up the red blood cells. Furthermore, it has been observed that if the blood sample is transferred to the sampling vial too rapidly, hemolysis can result. This in turn can cause a sharp rise or fall in test values. Additionally where plural samples are required, separate syringe assemblies are used requiring repuncturing of the vein which is undesirable and may result in aneurysm. The syringe method also presents the danger of injecting air into the patient which can cause undesirable clotting.
In other instances the blood sampling device comprises a cup-shaped holder which mounts a double ended needle, one needle projecting exteriorly of the holder which the nurse inserts in the vein, the other needle interiorly of the holder to receive a vacuum tube for collecting the blood sample. The inner needle is covered with a rubber sheath or shield which collapses accordion-style when the stopper of the vaccum tube is pierced to withdraw a first sample and which when the vacuum tube is removed reseals the needle. It has been found that these systems are only partially effective since the sheath does not always retract to a position to close the needle and stop the flow of blood from the vein. In these systems there is the possibility of return blood flow from the vacuum tube to the patient if the patient's blood pressure fluctuates and drops below that in the vacuum tube. Return flow can be dangerous since it may contain entrained unsterile matter or drug additives from the vacuum tube.
The one-way valve assembly of the present invention has particular application in blood collecting systems of this type and operates in a manner to preclude flow through the needle until the vacuum tube has been applied to the inner needle and closes immediately to prevent further blood flow when a filled tube is removed. The valve also responds to patient blood pressure and closes rapidly when veinal pressure drops below pressure in the vacuum tube thereby eliminating return of possibly contaminated blood from the vacuum tube to the patient. The valve precludes injection of air into the vein, minimizes loss of blood and controls flow in a manner minimizing damage to the blood cells.
The valve of the present invention has other useful applications in other medical and related fields such as venoclysis equipment and in systems for cultivating organisms.
Flow control valves for use in surgical apparatus or the like or in the administration of injection fluids are not new per se. Examples of valve systems in applications of this type are described in Zeddies et al U.S. Pat. No. 4,005,710; Cox U.S. Pat. No. 3,098,779; Nehring U.S. Pat. No. 3,469,572; German Pat. No. 2,349,996; Burke U.S. Pat. No. 3,021,841; Martinez U.S. Pat. No. 2,784,733; Beacham U.S. Pat. No. 2,844,147; and Abbott U.S. Pat. No. 2,538,662.
Of the patents listed above the Zeddies Pat. No. 4,005,710 is of particular interest. The Zeddies Patent shows a valve designed for use in an administration set consisting essentially of a conventional parenteral solution container with an air vented drip chamber connected through a tubing system including a Y-type injection site to a hyperdermic needle. The valve normally is open to permit flow of parenteral solution. If a second solution is introduced at a higher pressure than the parenteral solution, the valve is displaced to close flow of the parenteral. The valve is a disc-shaped element which has a plurality of projections depending from one face thereto. When the valve element is displaced in one direction for example downwardly, fluid flows from the inlet to the outlet through the spaces between the projections. In the raised position the valve normally seals the inlet opening and this condition exists when, for example, a second solution is introduced in the system through the inlet at a greater pressure than the pressure exerted by the fluid in the inlet. The valve height is substantially smaller than the axial depth of the cavity in which it is mounted to permit substantial axial movement when it is actuated between extreme limit positions and therefore there is a time lag when the valve moves between the limit positions.
The valve assembly of the present invention differs from the prior art and comprises a disc-like valve element made of a resilient flexible material such as rubber which has a plurality of circumferentially spaced axially projecting pedestals or legs projecting from one face thereof. This valve element is mounted in a housing having a valve chamber and is of a slightly smaller diametric dimension so that the valve contact with the sidewall of the valve chamber is limited. The housing has an inlet to the space above the upper face of the valve and an outlet at the opposite axial end of the valve cavity. The dimensional relationships and the valve chamber are such that the valve element is under predetermined compression in its normally closed position requiring a predetermined pressure at the inlet to unseat the valve element to permit flow from the inlet past the valve to the outlet. When used in a blood collecting system, the valve element remains closed at normal veinal pressures. In the preferred embodiment of the invention, a pair of cannulas project from the housing, one communicating with the inlet and the other with the outlet. The valve chamber has in the preferred arrangement a series of axial passages which are circumferentially spaced to define flow paths when the valve is displaced by either a pressure build up in the inlet which exceeds the pressure on the outlet side or a drop in pressure at the outlet side compared to the pressure at the inlet side. In applications where this assembly is used to draw blood from a vein, the nurse may insert one cannula or needle into the vein and by reason of the slight compression of the valve in the valve chamber, the inlet opening remains sealed. Now when it is desired to draw a sample, a vacuum tube having a pierceable stopper is engaged over the outlet needle or cannula which reduces the pressure sufficiently in the outlet chamber to effect downward deflection of the valve permitting flow of blood from the vein to the collection tube. It is noted that as the tube fills and the pressure balances, the valve closes. In this manner the nurse may remove the filled vacuum tube and insert another for additional withdrawal of blood without removing the device from the vein of the patient. If during the blood sampling cycle, patient blood pressure drops, the valve element closes rapidly thereby preventing flow of blood which may be contaminated back through the system into the patient.
A valve of the present invention, therefore, provides certain advantages over the prior art valves which may be broadly characterized as floating valve arrangements. This contrasts with the valve of the present invention wherein the valve element is under compression in the valve chamber so that the pressure differential required to open the valve may be controlled within very precise and controlled limits. Furthermore, the present invention provides the advantage of providing an effective seal in its normal closed position.